Process of making calcium cyanamid.



7 ing Calcium No Drawing.

other-mic, and one needs,

GEORGE E. COX, 0F NIAGARA FALLS, NEW YORK, ASSIGNOR TO AMERICAN CYANAMID COMPANY, OF NEW YORK, N. Y., A

CORPORATION OF MAINE.

PROCESS OF MAKING GALCI UIVI CYANAMID.

To all whom it may concern:

. Be it known that I, GEORGE E. Cox, a citizen of the United States, residing at Niagara Falls, in the county of Niagara and State of New York, have invented certain new and useful Improvements in Processes of Mak- Cyanar'nid; and I do hereby declare the following exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of improving the grade and of reducing the consumption of raw materials in the manufacture of commercial calcium cyanamid and has for its object to accomplish these results in a simple and efficient manner.

To these ends the invention consists in'the novel steps constituting the process, as will be more fully hereinafter disclosed, and particularly pointed out in the claims.

In order that thc precise invention may be the more clearly understood, it is said In the production of calcium cyanamid it has been a common practice to heat calcium carbid in a suitable container in a furnace adapted to the purpose. The furnace usually comprises a gas tight, metal shell, lined with a suitable sulating material. According to this invention the carbid may be charged into a foraminous vessel either outside the furnace, or preferablyinto said vessel when the latter is in place in said furnace. Nitrogen is next fed into the furnace, and surrounds the mass of finely divided carbid.

In order to start the absorptionof nitrogen by the mass of finely ground carbid, it is necessary ture of at least redness. T he reaction is extherefore, to heat only a portion of the carbid mass to the required reacting temperature, when the absorption of nitrogen begins, and the resulting evolved heat raises the rest of the mass to the required temperature for completing the nitrification. 1

It is customary to perform this initial heating of a portion of the carbid by a suitable resistor which on the passage of an electric cur-rent lwcolnes incandescent, and which by radiation or conduction, or both, transmits the necessary heat to the surrounding carbid, and thereby raises the latter to a re- Specification of Letters Patent.

to be a full, clear, andrefractory and heat 1nto heat the latter to a tempera- Patented Mar. 12, 1918;

Application filed December 19, 1917. Serial No. $07,963.

acting temperature. This resistor may be mserted directly into the mass of carbid, or

it may extend axially through a suitable opening in said mass.

It hasbeen heretofore the general practice, outside of the United States, to connect said resistor with a source of current at a constant potential and to regulate the adjusted voltage on the current carrying mains once for all, in order that with a given resistor, the proper amount of energy for starting the reaction will always be gener-' ated in said resistor.

, I have found, however,

.because a continuously larger quantity of carbid thus takes part in the reaction and evolves heat, and the solid cyanamid formed being a better heat conductor than the finely ground carbid, less and less quantities of heat are required from the resistor as the reaction proceeds. I

This varying quantity of heat required from the resistor for the most eliicient and rapid propagation of the reaction cannot well'be obtained from a source 0 constant potential, and therefore, wherever a constant potential has heretofore been eniployed in order to save current, the voltage has been adjusted to give less than the desired maximum energy at the start, and slightly more than the desired energy when the reaction has progressed substantially far enough to propagate itself through the remaining IIHISS Of carbid. But, such practice involves the objection that the voltage being lowerthan the desired maximum at the beginning, the reaction is slower in starting and propagating itself throughout the mass. And further, the voltage'being higher than the desired minimum after the reaction becomes self propagating, a waste of current ensues, as well as an objection- V that this practice of using a constant potential on thecurrent able melting, or fusing of a portion of the carbid, which prevents it from taking up nitrogen.

In order to avoid these objections, I temporarily, according to this invention, increase the impressed voltage on the resistor at the starting of the reaction and I then replace this temporarily increased voltage by a voltage somewhat lower than that formerly used, for the rest of the reaction.

I have also found that the use of an increased impressed'voltage at the start followed by a decreased impressed voltage for energy is supplied to the nitrifying oven, increases the efiiciency with which the nitrogen is used up. That is to say, it is a common practice to feed the nitrogen to the oven at a constant rate, so it follows that, heretofore, the voltage being below the desired maximum at the beginning of the reaction, the latter would not consume all the nitrogen present or in the early stages, and a'portiop therefore-be lost. On the other hand, by employing the temporarily increased voltage provided by this invention, the initial stages of the reaction are accelerated, a larger quantity of nitrogen present takes part in v the reaction, and a lesser quantity is lost) In addition to this, as above stated, owing to the employment heretofore of a voltage higher than the desired minimum after the reaction has fairly started, portions of the carhid were fused, nitrogen failed to permeate them, and a lower nitrifying efficiency resulted, than is the case when one follows this invention, and employs a voltage toward the end of the reaction too low to permit said fusion to any substantial extent, all as will be more fully hereinafter disclosed.

tated in other words, normal past prac tice requires a given period of time for completing the nitrification of a given batch of carbid. We may call this the total period of the reaction, and this total period varies with v the character of the furnace, the size of the mass of carbid, and its disposition in the furnace, as well as other minor conditions. For a portion only of this total reaction period is it necessary to supply energy from an outside source. This portion of the total period of reaction during which current is supplied may amount in time to say as much as one third of the said total reaction period, although this said time will also vary with the size ofthe batch of carbid and the design of the nitrification furnace. lln the usual practice, heretofore employed, where this energy was supplied electrically by means of a carbon resistor connected to electrical mains of constant po tential, for a given furnace I had under my charge, the reaction did not get well startthe main portion of the time during which messes penses, nterest, and other fixed charges- I The particular electrical conditions obtaining in this case permitted the generation of a certain quantity of energy in the furnace on closing the switch, this energy automatically increased to a maximum as the conductivity of the carbon resistor became better, and b the time the reaction had a good start in t .e oven, the energy had automatically increased to about 50% above that 1 obtaining at the closing of the switch which was a maximum, for it was about all that was allowable to maintain the reaction during its course without causing an undue overheating of the carbid.

According to this process, on the other hand, I make use of a portable transformer, orbooster to temporarily increase the impressed voltage on the resistor, at the starting of the heating period. With this apparatus I introduce, immediately on closing the switch, say about two and a half times the energy that the furnace receives under the old system. In a very few minutes the current so increases that I introduce say five times the energy of the older system reckoned at the same interval after throwing the switch. As a result, under this process, I get my furnace working and the reaction well started in a period not over 1/100 of the total time that energy is required to be supplied to the furnace. In other words, I have my furnace started and the reaction able to propagate itself in, say 1/20 of the time by my system that it takes to accomplish the same result when working under the old system of constant potential. As soon as nitrification is started, I disconnect the booster, and reconnect to the constant potential electrical mains, and furnish'energy as long as required, but at a" lower potcntial than heretofore direct from the said mains as in the older-system. I have further found that the quick andexcellent start obtained by this method under certain circumstances, permits me to operate at a normal line potential less than that used in the old system, for when the reaction gets a good start, the resistance of the charge is less and the heretofore.

It will now be clear that inall cases by following the procedure above outlined, I am enabled to obtain all the advantages of a rapid. start, without supplying an excessive amount of energy during those periods of the reaction when outside energy is still repotential can be lower than quired and that I thus not only avoid overheating and consequent loss of valuable carbid and nitrogen, but I also shorten the time of producin the product. In fact, it it safe to say, t s new process saves 5% of the total time required to nitrify the carbid, and possibly the same percentage of nitrogen over the old procedure.

The use of a transformer or booster as described above, is merely one example of a methodof carrying out the essential principles of the invention, and it is obvious that those skilled in the art may vary the details of the procedure without departing from the spirit of the invention, and therefore, I do not wish to be limited to the. above disclosure except as may be required .by the claims. What I claim is t 1. The process of making calcium cyanamid which consists in heating a mass of calcium carbid in the presence of .nitrogen and subsequently redilcing the quantity of heat supplied below that required to fuse a substantial portion of said carbid; maintaining said reduced supply of heat until the reaction is self-propagating; and continuing the reaction until substantially all the mass is converted into. cyanamid, substantially as. described.

2. The.process of making calcium cyanamid which consists in starting -a reaction between calcium carbid and nitrogen by supplying at first suliicient'energy'for attaining the desired start in a shorter period of time than has heretofore been customary; reducing thequantity of energy supplied for the remainder of the period during which energy is required; and continuing the reaction without any further addition of energy until substantially all the carbid has combined with nitrogen, substantially as described.

3. The process of making calcium cyanamid which consists in heating a mass of same;

action; feeding nitrogen at a calcium carbid to a reacting temperature; feeding nitrogen'to said mass at a constant rate; reducing the quantity of heat supplied to said mass after the reaction begins below that heretofore customary; maintaining the supplyof said reduced quantity of heat until the reaction becomes self propagating;

and continuing the reaction until the desired quantity of carbid has been nitrified, substantially as described.

l. The process of making calcium cyanamid which conslsts in supplying to a porand maintaining said reaction'until substan-.

all the carbid present has been nitritially lied, substantially as described.

5. The process of making calcium cyanamid which consists in supplying a finely divided mass of calcium carbid; providing a resistor for said mass capable of heating to a reacting temperature a portion of the supplying to said resistor current at reducing the 'temperature at which the'heat is supplied to a higher potential than hasheretofore been customary to start the reaction; feeding ni trogen to said mass; after the reaction starts supplying to said resistor current at a lower potential than has heretofore been customthen ar'y; and continuing the reaction until the desired quantity of calcium cyanamid has been produced, substantially as described.

In testimony whereof I afliX my signature,

presence of two witnesses.

GEORGE E. COX.

Witnesses THOS. J Con, C. H. Esnnmuan. 

